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1.
Free gas is ubiquitous at shallow sediment depths of the northern margin of the Gulf of Mexico. Gassy sediment patches are
between 250 and 500 m in horizontal size. Often the gassy layers are within 100 m from the sea floor and are only a few meters
thick. Both biogenic and thermogenic gas hydrates have been recovered. Stability values of temperature and pressure indicate
that hydrates can exist in water depths less than 500 m. Gassy sediment geoacoustic parameter values are not well constrained
because of a lack of concurrent measurements of acoustic properties and sediment gas content. For Gulf of Mexico gassy sediment,
some reportedin situ values of sound speed are reduced by an order of magnitude below values for water saturated sediments. More commonly, sound
speed is reduced from water saturated sediment values by only 15 to 50 percent. 相似文献
2.
This study aims to constrain the base of the hydrates stability field in structurally complexsites using the case of Woolsey Mound, a fault-controlled, transient, thermogenic hydrates system, in Mississippi Canyon Block 118, northern Gulf of Mexico. We have computed the base of the hydrates stability field integrating results from a recent heat-flow survey, designed to investigate geothermal anomalies along fault zones which exhibit different fluid flux regimes. An advanced “compositional” simulator was used to model hydrate formation and dissociation at Woolsey Mound and addresses the following hypotheses:
- 1.Migrating thermogenic fluids alter thermal conditions of the Hydrate Stability Zone (HSZ), so heat-flow reflects fault activity;
- 2.Gas hydrate formation and dissociation vary temporally at active faults, temporarily sealing conduits for migration of thermogenic fluids;
- 3.High salinity and inclusion of thermogenic gases with higher molecular weight than methane produce opposite effects on the depth to the bottom of the hydrate stability zone.
3.
R. Len L. Somoza C.J. Gimnez-Moreno C.J. Dabrio G. Ercilla D. Praeg V. Díaz-del-Río M. Gmez-Delgado 《Marine and Petroleum Geology》2009,26(8):1564-1579
This paper presents a computational model for mapping the regional 3D distribution in which seafloor gas hydrates would be stable, that is carried out in a Geographical Information System (GIS) environment. The construction of the model is comprised of three primary steps, namely: (1) the construction of surfaces for the various variables based on available 3D data (seafloor temperature, geothermal gradient and depth-pressure); (2) the calculation of the gas function equilibrium functions for the various hydrocarbon compositions reported from hydrate and sediment samples; and (3) the calculation of the thickness of the hydrate stability zone. The solution is based on a transcendental function, which is solved iteratively in a GIS environment.The model has been applied in the northernmost continental slope of the Gulf of Cadiz, an area where an abundant supply for hydrate formation, such as extensive hydrocarbon seeps, diapirs and fault structures, is combined with deep undercurrents and a complex seafloor morphology. In the Gulf of Cadiz, the model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic gas compositions, and explains the geometry and distribution of geological structures derived from gas venting in the Tasyo Field (Gulf of Cadiz) and the generation of BSR levels on the upper continental slope. 相似文献
4.
以墨西哥湾西北部陆坡区为研究区,利用NOAA/AVHRR热红外影像,通过分析1999年Central Mexico 7.0级地震、1999年Oaxaco 7.5级地震和2003年Colima 7.6级地震3次地震期间与墨西哥湾西北部陆坡区海底天然气水合物藏区对应的海表面上方卫星热红外亮温异常的变化,研究了卫星热红外亮温异常与深水海域天然气水合物藏区分布的关系.研究发现,与墨西哥湾西北部陆坡区海底天然气水合物藏区对应的海表面上方,临震前频繁出现孤立的、带状的、强度较大的卫星热红外亮温异常,该研究结果表明,同次和多次地震临震前,该地区频繁出现孤立、带状、强度较大的卫星热红外亮温异常可能与海底蕴藏着天然气水合物藏有关. 相似文献
5.
《Marine and Petroleum Geology》2013,39(1):128-142
The northern Gulf of Mexico is dominated by salt tectonics, resulting fracturing and numerous seafloor seeps and vents. Woolsey Mound, site of the Gulf of Mexico Hydrates Research Consortium's seafloor observatory, has been investigated extensively via surveys, direct sampling and seafloor instrument systems. This study presents an innovative approach to seismic data interpretation, integrating three different resolution datasets and maximizing seismic coverage of the complex natural hydrocarbon plumbing system at Woolsey Mound.3D industry seismic data reveal the presence of a salt body at in the shallow subsurface that has generated an extended network of faults, some extending from the salt body to the seafloor (master faults). Higher resolution seismic data show acoustic wipe-out zones along the master faults with expulsion features – seafloor pockmarks and craters – located immediately above them and associated, in the subsurface, with high-amplitude, negative anomalies at constant depth of 0.2 s TWTT b.s.f., interpreted as free gas. Since pockmarks and craters provide pathways for hydrocarbons to escape from depth into the water column, related sub-surface seismic anomalies may indicate free gas at the base of the gas hydrates stability zone (GHSZ). Fluid flow and gas hydrates formation are segmented laterally along faults. Gas hydrates formation and dissociation vary temporally in the vicinity of active faults, and can temporarily seal them as conduits for thermogenic fluids. Periodic migrations of gases and other fluids may perturb the GHSZ in terms of temperature and pressure, producing the observed lack of classical BSRs. 相似文献
6.
Northern Gulf of Mexico continental slope 总被引：1，自引：0，他引：1
The hummocky continental slope in the northwestern Gulf of Mexico is the result of active salt tectonism and accompanying
faulting. Fluid and gassy hydrocarbons rise through the sediment column and along faults causing the formation of gas hydrates,
gassy sediments, mud volcanoes and mounds, chemosynthetic communities and authigenic carbonates, reefs, and hardgrounds. Salt
activity coupled with processes associated with relative sea level fluctuations create a feedback relationship resulting in
the above-mentioned phenomena as well as others such as seafloor erosion at great water depths. 相似文献
7.
N. Satyavani 《Marine Georesources & Geotechnology》2013,31(3):191-201
The multichannel seismic data along one long-offset survey line from Krishna-Godavari (K-G) basin in the eastern margin of India were analyzed to define the seismic character of the gas hydrate/free gas bearing sediments. The discontinuous nature of bottom simulating reflection (BSR) was carefully examined. The presence of active faults and possible upward fluid circulation explain the discontinuous nature and low amplitude of the BSR. The study reveals free gas below gas hydrates, which is also indicated by enhancement of seismic amplitudes with offsets from BSR. These findings were characterized by computing seismic attributes such as the reflection strength and instantaneous frequency along the line. Geothermal gradients were computed for 18°C and 20°C temperature at the depth of BSR to understand the geothermal anomaly that can explain the dispersed nature of BSR. The estimated geothermal gradient shows an increase from 32°C/km in the slope region to 41°C/km in the deeper part, where free gas is present. The ray-based travel time inversion of identifiable reflected phases was also carried out along the line. The result of velocity tomography delineates the high-velocity (1.85–2.0 km/s) gas hydrate bearing sediments and low-velocity (1.45–1.5 km/s) free gas bearing sediments across the BSR. 相似文献
8.
An anomalous strong, shallow reflector has been observed in several deep-tow subbottom profiler records in a region of the northern Black Sea characterised by seafloor fluid seeps, mud volcanoes, and the occurrence of gas hydrates. The digital data were processed using adapted seismic processing methods. Synthetic seismograms created to model representative traces from the observed profiles require anomalous alternations of acoustic properties in the upper sediments which can best be explained by interbedded layers of normal sediments and sediments with gas hydrates. The enigmatic strong reflector can be explained by constructive interference of reflections from five of these thin layers. It is proposed that the uppermost region of the gas hydrate stability zone here is represented by thinning layers of interbedded gas hydrates or layers with lower concentrations of gas hydrates. 相似文献
9.
Impact of oil and gas vents and slicks on petroleum exploration in the deepwater Gulf of Mexico 总被引：2，自引：2，他引：2
Active petroleum vents and slicks have been identified in the deep water of the northern Gulf of Mexico using numerous techniques. The occurrence and distribution of these petroleum vents are strongly influenced by the local geological framework—especially the presence of vertical migration pathways into shallow sediments. Oil and gas vents may be more useful for establishing the existence of petroleum generation on a regional scale and for evaluating the gross properties of oil migrating in the subsurface than for appraising the exploration value of individual prospects. Knowledge about petroleum venting in the deepwater Gulf of Mexico has proven to be an important element of the successful exploration activities there. 相似文献
10.
A marine controlled source electromagnetic (CSEM) campaign was carried out in the Gulf of Mexico to further develop marine electromagnetic techniques in order to aid the detection and mapping of gas hydrate deposits. Marine CSEM methods are used to obtain an electrical resistivity structure of the subsurface which can indicate the type of substance filling the pore space, such as gas hydrates which are more resistive. Results from the Walker Ridge 313 study (WR 313) are presented in this paper and compared with the Gulf of Mexico Gas Hydrate Joint Industry Project II (JIP2) logging while drilling (LWD) results and available seismic data. The hydrate, known to exist within sheeted sand deposits, is mapped as a resistive region in the two dimensional (2D) CSEM inversion models. This is consistent with the JIP2 LWD resistivity results. CSEM inversions that use seismic horizons provide more realistic results compared to the unconstrained inversions by providing sharp boundaries and architectural control on the location of the resistive and conductive regions in the CSEM model. The seismic horizons include: 1) the base of the gas hydrate stability zone (BGHSZ), 2) the top of salt, and 3) the top and bottom of a fine grained marine mud interval with near vertical hydrate filled fractures, to constrain the CSEM inversion model. The top of salt provides improved location for brines, water saturated salt, and resistive salt. Inversions of the CSEM data map the occurrence of a ‘halo’ of conductive brines above salt. The use of the BGHSZ as a constraint on the inversion helps distinguish between free gas and gas hydrate as well as gas hydrate and water saturated sediments. 相似文献
11.
《Marine and Petroleum Geology》2012,35(1):111-118
Potential accumulations of gas hydrates in Alaminos Canyon Block 21 (AC21) in the Gulf of Mexico are thought to occur in a shallow sand-rich interval, stratigraphically separated from sources of free gas below the base of the gas hydrate stability zone (BGHSZ), by an intervening thick layer of clay- and silt-rich sediments. Availability of sufficient gas charge from depth, in addition to local biogenic sourcing is considered key to the formation of gas hydrates in the GHSZ. Implicitly, a detailed understanding of geometries associated with fault and fracture networks in relation to potential gas migration pathways can provide additional confidence that seismic amplitude anomalies are related to gas hydrate accumulations. Delineation of fault and fracture systems from high resolution seismic data in and below the gas hydrates stability zone (GHSZ) was performed using an automated algorithm—Ant Tracking. The capturing of small-scale detail has particular significance at AC21, revealing a pervasive network of typically small-extent discontinuities, indicative of fracturing, throughout this intervening clay- and silt-rich layer of mass-transport deposits (MTDs). Ant Tracking features appear to correlate, to some extent, with potential gas hydrate accumulations, supporting the concept that fracturing possibly provides migration pathways albeit via a tortuous, complex path. This study demonstrates that the Ant Tracking attribute, in conjunction with detailed seismic interpretation and analysis, can provide valuable evidence of potential gas migration pathways. 相似文献
12.
Seismic expression of sedimentary volcanism on the continental slope,northern Gulf of Mexico 总被引：2，自引：1，他引：2
High-resolution geophysical data define acoustically amorphous, mounded structures on the upper, middle, and lower continental
slope of the northern Gulf of Mexico. Physical samples and observations within this unique seismic facies show gassy sediments,
sometimes in hydrated form and, in places, as chemosynthetic communities. The geologic setting of these mounds suggests that
the process of formation falls on the continuum of mud volcanoes to mud diapirs. 相似文献
13.
《Marine and Petroleum Geology》2012,35(1):4-30
The northern Gulf of Mexico (GoM) has long been a focus area for the study of gas hydrates. Throughout the 1980s and 1990s, work focused on massive gas hydrates deposits that were found to form at and near the seafloor in association with hydrocarbon seeps. However, as global scientific and industrial interest in assessment of the drilling hazards and resource implications of gas hydrate accelerated, focus shifted to understanding the nature and abundance of “buried” gas hydrates. Through 2005, despite the drilling of more than 1200 oil and gas industry wells through the gas hydrate stability zone, published evidence of significant sub-seafloor gas hydrate in the GoM was lacking. A 2005 drilling program by the GoM Gas Hydrate Joint Industry Project (the JIP) provided an initial confirmation of the occurrence of gas hydrates below the GoM seafloor. In 2006, release of data from a 2003 industry well in Alaminos Canyon 818 provided initial documentation of gas hydrate occurrence at high concentrations in sand reservoirs in the GoM. From 2006 to 2008, the JIP facilitated the integration of geophysical and geological data to identify sites prospective for gas hydrate-bearing sands, culminating in the recommendation of numerous drilling targets within four sites spanning a range of typical deepwater settings. Concurrent with, but independent of, the JIP prospecting effort, the Bureau of Ocean Energy Management (BOEM) conducted a preliminary assessment of the GoM gas hydrate petroleum system, resulting in an estimate of 607 trillion cubic meters (21,444 trillion cubic feet) gas-in-place of which roughly one-third occurs at expected high concentrations in sand reservoirs. In 2009, the JIP drilled seven wells at three sites, discovering gas hydrate at high saturation in sand reservoirs in four wells and suspected gas hydrate at low to moderate saturations in two other wells. These results provide an initial confirmation of the complex nature and occurrence of gas hydrate-bearing sands in the GoM, the efficacy of the integrated geological/geophysical prospecting approach used to identify the JIP drilling sites, and the relevance of the 2008 BOEM assessment. 相似文献
14.
Peter H. Santschi Gilbert T. Rowe 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2572
Sedimentation rates were determined for the northern Gulf of Mexico margin sediments at water depths ranging from 770 to 3560 m, using radiocarbon determinations of organic matter. Resulting sedimentation rates ranged from 3 to 15 cm/kyr, decreasing with increasing water depth. These rates agree with long-term sedimentation rates estimated previously using stratigraphic methods, and with estimates of sediment delivery rates by the Mississippi River to the northern Gulf of Mexico, but are generally higher by 1–2 orders of magnitude than those estimated by 210Pbxs methods. Near-surface slope sediments from 2737 m water depth in the Mississippi River fan were much older than the rest. They had minimum 14C ages of 16–27 kyr and δ13C values ranging from −24‰ to −26.5‰, indicating a terrestrial origin of organic matter. The sediments from this site were thus likely deposited by episodic mass wasting of slope sediment through the canyon, delineating the previously suggested main pathway of sediment and clay movement to abyssal Gulf sediments. 相似文献
15.
Stable isotope ratios (δ13C) of total organic carbon were measured in surface sediments from the continental margins of the northern and western Gulf of Mexico, the north coast of Alaska and the Niger Delta. Gulf of Mexico outer-shelf isotope ratios were in the same range as has been reported for Atlantic coastal shelf sediments, ?21.5 to ?20‰. Off large rivers including the Mississippi, Niger and Atchafalaya (Louisiana), δ13C values increased from terrigenous-influenced (around ?24‰) to typically marine () within a few tens of kilometers from shore. This change was accompanied by a decrease in the amount of woody terrigenous plant remains in the sediment. Alaskan continental margin samples from the cold Beaufort Sea had isotopically more negative carbon (?25.5 to ?22.6‰) than did warmer-water sediments. The data indicate that the bulk of organic carbon in Recent sediments from nearshore to outer continental shelves is marine derived. 相似文献
16.
Stephan A. Klapp Gerhard Bohrmann Werner F. Kuhs M. Mangir Murshed Thomas Pape Helmut Klein Kirsten S. Techmer Katja U. Heeschen Friedrich Abegg 《Marine and Petroleum Geology》2010
Gas hydrate samples from various locations in the Gulf of Mexico (GOM) differ considerably in their microstructure. Distinct microstructure characteristics coincide with discrete crystallographic structures, gas compositions and calculated thermodynamic stabilities. 相似文献
17.
Jiliang Wang Shiguo Wu Jianhua Geng Priyank Jaiswal 《Marine Geophysical Researches》2018,39(4):509-522
A better understanding of wave attenuation in hydrate-bearing sediments is necessary for the improved geophysical quantification of marine gas hydrates. Here we compare the attenuation behavior of hydrate-saturated vs water-saturated sediments at site GC955H, in the Gulf of Mexico, which was surveyed during the JIP Leg II expedition. We compute the P-wave attenuation of the gas hydrate bearing sediments using the median frequency shift method on the monopole waveforms. The results show that P-wave attenuation due to low saturation (<?0.4) in hydrate-filled fractures of fine-grained sediment is comparable to that of the water-filled fracture case. On the contrary, P-wave attenuation due to high saturation (>?0.4) in the hydrate-filled pores of coarse-grained sediments can be up to as much as three times more than that of the water-saturated case. The correlation analysis shows that the P-wave attenuation increases with the increasing gas hydrate saturation for the highly saturated gas hydrate-bearing sand interval while the correlation of the P-wave attenuation and hydrate saturation is weak for low saturated gas hydrate-bearing shale interval. The results show that P-wave attenuation is more likely to be used as a geophysical proxy for gas hydrate quantification of highly concentrated coarse-grained sediment rather than for that of fine-grained sediment. To examine the P-wave behavior in sand, we use the improved LCAM model, which accounts for physical factors such as grain boundary roughness and squirt flow to explain the observed differences in P-wave attenuation between hydrate and water-saturated coarse-grained sediment. Our results provide further geophysical evidences for P-wave behavior in the gas hydrate-bearing sediments in the field. 相似文献
18.
We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show high-reflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (<1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data.We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km2) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as ‘chimney’ features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes. 相似文献
19.
南海北部天然气水合物研究进展 总被引：11，自引：0，他引：11
天然气水合物是一种新型的储量巨大的绿色能源,是目前世界各国研究界的研究热点之一。我国以及美国、日本、印度、韩国等国家都采集到了天然气水合物的实物样品。虽然我国对天然气水合物的研究起步较晚,但近年来的研究已经取得了飞速的进步,而且也于2007年5月在南海北部陆坡的神狐海域成功采集到天然气水合物的实物样品,这是在南海海域首次获取天然气水合物实物样品,证实了南海北部蕴藏着丰富的天然气水合物资源,标志着我国天然气水合物调查研究水平又上了一个新的台阶。目前,南海北部陆坡已经作为我国天然气水合物未来开发的战略选区之一。在总结我国天然气水合物以往十几年研究工作的基础上,综述了我国天然气水合物近年来在南海北部的地质、地球物理、地球化学3个方面的研究进展,提出了未来天然气水合物勘探和研究的方向和建议。 相似文献
20.
The continental slope off Texas and Louisiana is the most structurally and sedimentologically complex area in the Gulf of
Mexico. This 120,000 km2 area is dominated by diapiric tectonics, resulting in numerous faults, oil and gas seeps, and other geological phenomena
that affect near-surface sediments. Bottom gradients range from 0 to 20°. High-resolution seismic surveys, foundation borings,
and drop cores reveal several mass-movement features, acoustic wipeout zones, sea floor erosion, faults, hardgrounds, bioherms,
reefs, and outcrops. Recent data indicate that most geological activity takes place during relative sea level lowering and
low stands. 相似文献